Lino still uses ExtJS version 3, which is rather old.

The main reasons for this are that everybody is happy with the user interface as it is right now (well, at least the end-users), and that it is not trivial because Sencha made important backwards-incompatible changes in version 4.

The basic plan is simple: create a lino.modlib.extjs6 as a copy of
lino.modlib.extjs, then adapt the linoweb.js, then adapt ext_renderer.py. This work is started at [url github.com/lsaffre/lino_extjs6]

The challenge is that the user interface is a rather complex beast after all. My estimation is that this will take more than a man month to me.